Express your answer as a mixed number simplified to lowest terms. $15\dfrac{18}{20}-12\dfrac{8}{12} = {?}$
Solution: Separate the whole numbers from the fractional parts: $= {15} + {\dfrac{18}{20}} - {12} - {\dfrac{8}{12}}$ Bring the whole numbers together and the fractions together: $= {15} - {12} + {\dfrac{18}{20}} - {\dfrac{8}{12}}$ Subtract the whole numbers: $=3 + {\dfrac{18}{20}} - {\dfrac{8}{12}}$ Simplify each fraction: $= 3 + {\dfrac{9}{10}} - {\dfrac{2}{3}}$ Find a common denominator for the fractions: $= 3+\dfrac{27}{30}-\dfrac{20}{30}$ Subtract the fractions: $= 3+\dfrac{7}{30}$ Combine the whole and fractional parts into a mixed number: $= 3\dfrac{7}{30}$